1. Field of the Invention
The invention relates to a method of position detection in X-ray imaging as well as to a device for carrying out such a method which includes an X-ray apparatus, a detector device, comprising at least two detector elements, and an indicator device.
2. Description of Related Art
A device for position detection in medical imaging is described in WO 97/40763. Therein, two cameras which are capable of detecting visible light or infrared light are connected to a stand so as to be stationary in space. Diodes which emit light that can be detected by the cameras are attached to a treatment instrument. The position of the treatment instrument in a co-ordinate system which is coupled to the cameras can be determined by means of the cameras. This position can be converted into an image position by means of a predetermined transformation matrix, the image having been formed in advance by means of computer tomography (CT) or magnetic resonance (MR) tomography. In order to determine said transformation matrix for converting camera coordinates into image co-ordinates, markers are provided on the patient during the image acquisition; these markers are also reproduced so that they are visible in the image. The treatment instrument provided with diodes, or a separate indicator instrument provided with diodes, is subsequently moved to these markers so that the position thereof is determined in camera co-ordinates. This establishes the necessary link between camera co-ordinates and image co-ordinates and enables the position of the treatment instrument to be reproduced in the image during a treatment.
The exact association of a point in an X-ray image with a point in or on an object to be examined may also be very important in conventional X-ray imaging, notably in the case of intra-operative imaging. The exact determination of the position of a treatment instrument or another medical apparatus, for example a radiation therapy apparatus, is also desirable. According to the known method it is necessary to provide the object to be examined with markers in fixed positions for a prolonged period of time, i.e. already upon the image acquisition by means of CT or MR and later upon the position detection by means of the cameras. The mounting of the cameras on a stationary stand is not ideal either for position detection during X-ray imaging. It is notably in the case of intra-operative X-ray imaging by means of a pivotable X-ray apparatus that the lines of sight of the camera are often obscured by the X-ray apparatus itself or by the attending staff when the cameras are mounted in this manner.